The invention relates to a method of building from refractory bricks a refractory structure or part of such a structure, which while being heated to working temperature and/or built is subject to local differences in thermal expansion and measures are taken to counterbalance these differences.
Although the invention will chiefly be explained with reference to its application to the construction and repair of coking chamber walls, it is not restricted to this.
When building new refractory structures and in particular coking chambers, allowance should be made for considerable and frequently uneven thermal expansion of the refractory structure. This particularly holds good if silica, which is commonly used for coking chambers, is used as the material for the shaped bricks. This is the result of the very pronounced and uneven expansion behaviour of silica even at low temperatures. In the past measures have been suggested to remedy the harmful results of this expansion, by continuously seeking solutions involving expansion joints being built in between larger parts of the structure.
A drawback of this method consists in that uneven expansion cannot be counterbalanced sufficiently in this way, and that consequently local damage may occur. Besides, the large movements of parts of the structure result in structural problems in counterbalancing these movements.
It is often common practice in repair work to coking chamber walls to employ spraying methods. However, if the damage to the brickwork of a coking chamber wall becomes too great it is no longer sensible to apply such spraying methods and generally speaking the damaged wall or just the damaged brickwork in this wall will be partially or completely replaced. Cooling of a complete coking chamber for carrying out a comparatively small repair job itself results in substantial damage to the brickwork. For this reason such repair jobs are frequently performed in such a way that the parts of the wall which need not be repaired are kept at the required temperature. In principle it is preferable to lay the new bricks bonded to the remaining old parts of the wall in order to achieve as stable a wall structure as possible.
The difficulty arising here is the fact that the still hot existing brickwork has already expanded, while the new and cold masonry will expand as it is heated to the same temperature. This results in damage not only to the new brickwork, but also to the existing brickwork and to its adhesion. These drawbacks are in particular felt if the wall consists of silica bricks, which exhibit a particularly uneven and large thermal expansion.
All kinds of suggestions have been made to solve the problems of the uneven thermal expansion between the existing and the new brickwork but so far without obtaining a generally satisfactory solution. For instance the suggestion has been made to apply compressible mortar masses. However, the result is a structure which differs locally from the remainder of the brickwork, while it is also evident that the uneven expansion of the replacement brickwork cannot be sufficiently counterbalanced by using compressible types of mortar.
It is also evident that in brick-laying with such types of mortar the supporting function of the replacement brickwork is insufficient if it must for example support an oven deck of a coking chamber. This eventually necessitates the use of additional expensive and complicated aids to support the oven deck. Another suggestion made is to build the replacement brickwork into the existing wall with joints or cavities in order to be able to make up for thermal expansion of the replacement material. However, as a result of uneven expansion of the replacement brickwork gaps occur in the brickwork in this manner, which are particularly objectionable in a coking chamber. It is also clear that the uneven expansion of the replacement brickwork cannot be sufficiently counterbalanced while the chamber is being heated on account of joints between the replacement brickwork and the existing brickwork.
Besides, by failing to bond the bricks connecting the existing and replacement brickwork, a structure results without much stability. It has been suggested previously to obtain the required bond despite this by making the bricks employed at the region of connection thinner and to apply in those places thicker, and if required compressible, joints.
Proposals have also been made (U.S. Pat. No. 2,985,442 and U.K. Pat. No. 1 298 079) to provide expansion joints by the use of cardboard or pasteboard inserts which burn away when the brickwork is heated. In the case of U.K. Pat. No. 1 298 079 it is suggested that such inserts may be put in occasional ones of successive joints between bricks of a refractory brickwork lining to permit expansion of the bricks when the inserts have burned away. However, these inserts are insufficient to provide the necessary expansion of the brickwork as they can be spaced no closer than every fifth joint, because the gaps left when they have burned away are prevented by friction from closing properly and more of such inserts would therefore prevent the formation of a tight brickwork lining. The major part of the necessary thermal expansion must therefore be accommodated by a loose packing of a compressible material, which can lead to problems as already explained above.